Reduced urinary levels of angiotensin-converting enzyme 2 activity predict acute kidney injury in critically ill patients

Objective: Angiotensin-converting enzyme 2 activity reflects non-classical renin–angiotensin system upregulation. We assessed the association of urinary angiotensin-converting enzyme 2 (uACE2) activity with acute kidney injury (AKI). Design, setting and participants: A prospective observational study in which we measured uACE2 activity in 105 critically ill patients at risk of AKI. We report AKI stage 2 or 3 at 12 hours of urine collection (AKI(12h)) and AKI stage 2 or 3 at any time during intensive care unit stay in patients free from any stage of AKI at inclusion (AKI(ICU)). AKI prediction was assessed using area under the receiver-operating characteristics curve (AUROC) and net reclassification indices (NRIs). Main outcome measure: AKI stage 2 or 3 at 12 hours of urine collection. Results: Within 12 hours of inclusion, 32 of 105 patients (30%) had developed AKI(12h). Corrected uACE2 activity was significantly higher in patients without AKI(12h) compared with those with AKI(12h) (median [interquartile range], 13 [6–24] v 7 [4–10] pmol/min/mL per mmol/L of urine creatinine; P < 0.01). A 10-unit increase in uACE2 was associated with a 28% decrease in AKI(12h) risk (odds ratio [95% CI], 0.72 [0.46–0.97]). During intensive care unit admission, 39 of 76 patients (51%) developed AKI(ICU). uACE2 had an AUROC for the prediction of AKI(12h) of 0.68 (95% CI, 0.57–0.79), and correctly reclassified 28% of patients (positive NRI) to AKI(12h). Patients with uACE2 > 8.7 pmol/min/mL per mmol/L of urine creatinine had a significantly lower risk of AKI(ICU) on log-rank analysis (52% v 84%; P < 0.01). Conclusions: Higher uACE2 activity was associated with a decreased risk of AKI stage 2 or 3. Our findings support future evaluations of the role of the non-classical renin–angiotensin system during AKI.